1. The Field of the Invention
The present invention is related to a tool for extracting helical coils ("helicoils") from threaded holes. More particularly, the present invention is related to a tool which is capable of wedging the end of the helicoil away from the thread and then securely capturing said end and twisting it out of a threaded hole in such a manner as to generally contract the helicoil inwardly toward its longitudinal axis.
2. Technical Background
Helicoils are a commonly used in the repair and refurbishing of mechanical mechanisms. In many situations it is common for threaded holes to be damaged such that the threads are no longer in their original usable condition. For example, it is common for a bolt placed within a threaded hole to become lodged. Removal of the bolt may require the application of forces sufficient to damage the threads within the threaded hole. Alternatively, simple wear and tear may eventually result in sufficient damage to the threads within a hole that they will no longer satisfactorily perform their intended functions.
Once a set of threads is damaged, however, there are a limited number of steps that can be taken in order to reuse or replace the mechanical part which includes a threaded hole. One alternative is clearly to discard the part. This alternative is only practical, however, when the part is relatively inexpensive and replacement parts are readily available. In the case of damaged threads included on large, complex, or expensive pieces of machinery, it may not be practical to simply replace the part. Rather, refurbishing of the part may be required.
One method of partially repairing the damaged threads involves drilling out the damaged threaded hole and then rethreading the new larger hole. It is obvious, however, that the new hole will no longer be capable of holding a bolt of the same size as the original hole. In order to solve this problem, it is conventional to insert a helicoil into the newly threaded hole.
A helicoil is, as the name would suggest, essentially a coiled helix. Such a device is shaped in the same general manner as a coiled spring. The coil is inserted into the newly threaded hole by first winding or compressing the coil in the same manner as a coil spring would be wound. Specialized tools are commercially available for winding the helicoil for insertion. The diameter of the coil is reduced during the winding step, providing for easy insertion of the coil into the threaded hole. When the insertion tool is removed, the coil unwinds and expands, seating the coil into the parent threads. Thus, the coil engages the parent threads through friction.
Once the helicoil is secured in place, it is possible to insert a bolt of the same size previously used in the device because the gap between the bolt and the threads is filled by the helicoil. Thus, it is not necessary to replace the device having the damaged threads, or to resort to a larger sized bolt. As was mentioned above, this mechanism is used in many different contexts, from small engines to very large and complex machinery.
One problem that has been frequently encountered in the use of a helical coil insert is difficulty in removal of the coil from the threaded hole after insertion. It is often necessary, over the life of a piece of machinery, to remove and replace the helicoil inserted within the threaded hole. Reasons for removal of the helicoil may include damage to the helicoil during use, or a need to fully refurbish the mechanical part in which the helicoil is seated.
It is conventional in the art to remove helicoils by using a standard wedge-shaped extraction tool. The extraction tool is wedged down into the interior of the threaded hole until it engages the helicoil. The wedge is generally provided with sharpened edges which are driven into the inside diameter of the first coil thread. Once the tool has engaged the coil the tool is twisted in the appropriate direction to back the helicoil out of the threads.
It will be appreciated that this type of tool has serious drawbacks in extracting the helicoil. The primary drawback relates to the direction of the forces exerted on the helicoil. In order for the wedge to securely engage the helicoil, a force is exerted outwardly from the radial axis of the helicoil. This outward force results in the application of additional pressure at the junction between the helicoil and the thread. Thus, an additional counteracting force is introduced during extraction which tends to damage the parent threads and to make extraction much more difficult.
Thus, it would be an advancement in the art to provide a tool for extraction of helicoils which overcomes the drawbacks of existing extraction tools. More particularly, it would be an advancement in the art to provide a helicoil extraction tool which was capable of extracting helicoils without the necessity of wedging the tool into the interior of the helicoil thus minimizing damage to the parent threads and additional forces opposing extraction. It would be an advancement in the art to provide such a removal device which was capable of drawing the helicoil away from the parent thread. It would be a related advancement in the art to provide such a device which tended to generally reduce the diameter of the helicoil during extraction.
Such an apparatus is disclosed and claimed herein.